The present invention relates generally to a mass exchanger and method of making a mass exchanger. As used herein, the term xe2x80x9cmass exchangerxe2x80x9d is defined as an apparatus wherein solute molecules in a solvent pass from the solvent to a mass transfer medium, or particles in a fluid pass from the fluid to a mass transfer medium.
Mass transfer has been well known and studied for many years. Examples include chemical separations, catalytic reactions wherein a species contacts a catalyst surface and exchanges mass with another species to form a compound, i.e. catalytic reaction. Exemplary apparati include kidney dialysis machines for separations wherein the mass transfer medium is a tube through which certain compounds pass because of a concentration gradient from the fluid within the tube to the fluid exterior to the tube. An example of a catalyzed mass transfer apparatus is a catalytic converter to reduce pollutants in automobile exhaust. Disadvantages of large scale mass transfer have been recognized and efforts made to use small scale mass transfer.
Separations and catalyzed reactions have been shown in microscale apparati as well. U.S. Pat. No. 5,534,328 to Ashmead et al. show a laminated structure wherein flow channels are made by etching a laminate partially through its thickness and stacking another laminate upon it to form a flow channel. Header holes through the laminate thickness are provided for inlets and outlets. Ashmead et al. suggest incorporating catalytic activity by packing a segment of a channel with catalytic beads or depositing catalytic materials onto the surface of a channel. Ashmead et al. further suggest mixer chambers formed by a half channel etched on the bottom of one laminate in combination with a half channel on the top of another laminate. A disadvantage of the construction of Ashmead et al. is the complexity and expense of carving laminates partially through the thickness of the laminates. A further disadvantage of the construction of Ashmead et al. is the small aspect ratio of width to depth of their channels for flow resistance and pressure drop. The construction of Ashmead et al. cannot achieve diffusive mass transfer, or controlled mixing by actuation.
Thus, there remains a need for a microchannel mass exchanger having a lower cost of fabrication and which provides a reduced pressure drop.
The present invention is a mass exchanger and method of making it. The method of making a microchannel mass exchanger, has the steps of:
(a) forming at least one inner thin sheet having a solid margin around a circumference, the solid margin defining a slot through a thickness;
(b) forming at least one outer thin sheet having at least two header holes positioned within the solid margin and positioned at opposite ends of a slot length, wherein the at least one inner thin sheet is placed adjacent the at least one outer thin sheet, the solid margin sealably spacing the at least one outer thin sheet the at least one outer thin sheet defining at least one longitudinal wall of a flow channel having a length parallel to a thin sheet length, wherein a fluid enters through one of the header holes into the slot to flow in a direction parallel or longitudinal to the length of the flow channel and exits through another of the header holes;
(c) placing a mass transfer medium on at least one of the outer thin sheet within the solid margin;
(d) stacking the at least one inner thin sheet in contact with the at least one outer thin sheet into a stack and placing an end block on the at least one inner thin sheet as a pre-bonded assembly; and
(e) bonding the pre-bonded assembly into the microchannel mass exchanger.
The apparatus of the present invention is a microchannel mass exchanger, having:
(a) at least one inner thin sheet having a solid margin around a circumference, the solid margin defining a slot through a thickness;
(b) at least one outer thin sheet having at least two header holes positioned within the solid margin and positioned at opposite ends of a slot length, wherein the at least one inner thin sheet is placed adjacent the at least one outer thin sheet, the solid margin sealably spacing the at least one outer thin sheet, the at least one outer thin sheet defining at least one longitudinal wall of a flow channel having a length parallel to a thin sheet length, wherein a fluid enters through one of the header holes into the slot to flow in a direction parallel or longitudinal to the length of the flow channel and exits through another of the header holes;
(c) a mass transfer medium on at least one of the at least one outer thin sheet within the solid margin;
(d) the at least one inner thin sheet in contact with the at least one outer thin sheet into a stack with an end block on the at least one inner thin sheet as a pre-bonded assembly; and
(e) the pre-bonded assembly bonded into the microchannel mass exchanger.
An advantage of the present invention is that the slot may have a large aspect ratio of its width to its depth or thickness. Another advantage of the present invention is that it accommodates a variety of materials including materials not amenable to bulk or surface micromachining, for example ceramics. A further advantage is that the method may be used in high volume production which is a key to economical and commercially viable products.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.